For the average person, the astrophysics involved in the earth's single-star solar system may be difficult enough to grasp, but for a pair of planet-hunting citizen scientists and a group of international researchers taking part in a Yale University-led project that recently uncovered a new planet, one-star systems are just the tip of the iceberg.

The research team, which includes Dirk Terrell, a Boulder-based astrophysicist with the Southwest Research Institute, earlier this year identified and confirmed the existence of the first known planet orbiting twin suns in a distant star system that is in turn orbited by a second set of distant stars.

The planet, dubbed PH1, is what scientists are calling a circumbinary planet in a four-star system and is the subject of a paper presented Monday at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno, Nev. It is one of only seven known planets in circumbinary star systems -- where the two central stars orbit one another -- and the only one in a system with two other orbiting stars, researchers say.

"It goes to the extremes of planet formation," said Meg Schwamb, an astronomy and astrophysics postdoctoral fellow at Yale who was the lead author of the paper on PH1 and a co-founder of the Planet Hunters project that lead to the discovery. "We don't truly understand how planets form around these stars."

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PH1 was first spotted by a pair of "armchair astronomers" who were analyzing data from NASA's Kepler spacecraft on the PlanetHunters.org website that invites citizen scientists to try their hand at spotting patterns in data that might otherwise go unnoticed. Schwamb notes the human brain has tremendous capacity for spotting patterns and sometimes people pick up patterns in data that machines miss.

"The way the Kepler satellite works is it measures the brightness of stars, very, very accurately," explained Terrell, who has 20 years of experience in astrophysics and primarily studies binary star systems.

Terrell said Kepler keeps data on the light curves it observes from distant stars. When the light curve dips, or vibrates slightly, it is a sign of an object passing before the star, which sometimes indicates the presence of an orbiting planet.

Earlier this year, Planet Hunters volunteers Kian Jek of San Francisco and Robert Gagliano of Cottonwood, Ariz., were analyzing light data from PH1's two parent stars when they noticed faint dips in the light caused by the planet. They alerted the research team to their observations, which lead to verification work and eventually the paper presented Monday.

"It's a great honor to be a Planet Hunter, citizen scientist, and work hand-in-hand with professional astronomers, making a real contribution to science," Gagliano said in a new release issued by Yale.

Schwamb lauded Jek and Gagliano for spotting the light patterns created by PH1, noting the difficulties in making such observations.

Schwamb was working to verify Jek and Gagliano's observations in March when she made a visit to the offices of the Southwest Research Institute's Boulder-based Space Studies and Spacer Operations Departments and ended up meeting with Terrell.She said he did a great job modeling the light curve data coming from the system to show the pattern created by the almost imperceptible transits of PH1 across its parent stars.

"I dug into it for a few days, and I found that yes indeed they did have a planet in this system," Terrell said.

After Terrell helped confirm the existence of PH1, researchers utilized the Keck telescopes in Mauna Kea, Hawaii, some of the most powerful telescopes in the world, to zero in on the system and learn more about it.

So far, using all the data they have been able to collect, researchers have determined that PH1 is a gas giant and its radius appears to be a little more than six times that of the Earth, or slightly smaller than Neptune or Uranus.

The two stars at the center of the system are roughly 1.5 and 0.4 times the mass of the sun, and while they both technically orbit their combined center of mass, the larger star is much closer to the center and the smaller star effectively orbits it every 20 days, with PH1 orbiting them every 138 days. The pair of distant stars in the system are roughly 1,000 astronomical units away from the central binary, or 1,000 times the distance between the Earth and the sun.

Terrell said this discovery will have a powerful impact on the way binary stars systems are regarded by researchers, and astronomers will have to look very carefully at how planets form in conditions like that of PH1.

"There are lots of binaries but only a handful of planets have been discovered," he said. "This has all kinds of implications for how planets form in multiple star systems."

With research funding being very hard to come by in the field, Terrell applauded the efforts of citizen scientists like Jek and Gagliano in helping make such discoveries. He said it's hard to predict when a discovery like that of PH1 may have much wider-ranging scientific implications, which is why it is important to continue looking to the stars.

"You just never know," Terrell said. "You explore, you try to understand things and try to know as much as you can so when the situation arises, you are able to make use of it."

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